Color-imaging systems known in the art permit images to be captured by certain image-receptive media or devices, possibly digitized and stored, and then output onto a complementary medium. For example, color images may be first captured on negative film and then reproduced on negative photographic paper. Such images may or may not pass through a digital intermediary.
In another example, color images may be captured on positive photographic materials, known as transparencies, and then viewed directly by projection or back-illumination, or copied onto larger or smaller transparencies, or printed onto positive photographic paper. Again, such images may or may not pass through a digital intermediary.
In yet another example, color images may be captured as an electronic signal by a video camera, and then viewed on a video monitor or converted to print by a device such as a thermal printer. Again, such images may or may not pass through a digital intermediary.
The foregoing are a few examples of color-imaging systems. The application of this invention is not limited to the above examples, but may be applied to other color-imaging systems as well, for instance to the reproduction of reflection originals using photographic or electrostatic means.
Color-imaging systems in which the image passes through a digital intermediary allow improvements to be made to the image using a single means which may be a digital computer. Thus, improvements to the image's color and tone scale can be made in a convenient and adaptable way. Furthermore, if combined with a means for rapid viewing of the changes, the content of the image can also be edited in a convenient fashion. Many of these improvements are known to those skilled in the art.
For example, U.S. Pat. No. 4,500,919 entitled "COLOR REPRODUCTION SYSTEM" by W. F. Schreiber, discloses an image reproduction system in which an electronic reader scans an original color image and converts it to an electronic image. A computer workstation and an interactive operator interface, including a video monitor, permit an operator to edit the image by means of one or more color image mappings or transformations. When the operator has composed a desired image on the monitor, the workstation causes an output writing device to make an inked output of the reproduced image.
A color-imaging system may contain a stored transform defined for each image-data mapping or transformation. Based on a selected transform definition, the system effectively maps pixel values from one image data metric to new values either in the same image data metric, or from one image data metric to another image data metric. Accordingly, the values of each pixel of a digital image are mapped in accordance with the transform definition. To perform another image transformation, the system may again remap the values to yet other values in accordance with a second transform definition. Any number of transformations can thus be performed by sequentially mapping values according to the available predetermined transform definitions. However, such sequential processing of images can be extremely time consuming, particularly if a large number of predetermined transforms are required.
Thus, an improved color-imaging system would have the ability to combine a plurality of stored transform definitions into a single composite transform. For example, each of the steps required to form a digital intermediary from input image data may require an individual stored transform. However, if each of the transforms is linear or approximately linear, they can be combined to form a single composite transform which can then be applied to the digital image data to obtain the same result as sequentially applying the individual transforms. In many cases, the composite transform can be formed in advance and stored, thus reducing the amount of processing time.
An improved color-imaging system would further provide the capability to produce, from input images transformed from various media or sources to a digital intermediary, appropriately rendered output images on any of a number of output or display means using an output transform between the digital intermediary and the selected output or display means, wherein the output transform is independent of the input image medium or source. In each case, images would be rendered in a way that is appropriate based on the capabilities and limitations of the specific output device and/or medium and on the specific application for which the image is being produced. With this capability, images from disparate input sources such as negative films, positive films, various reflection media, video cameras, and other electronic imaging means, which have been transformed to the digital intermediary, can be output to a selected imaging means using the same transformation between the digital intermediary and the selected imaging means regardless of the input image origins.
An improved color-imaging system would additionally provide the capability to combine portions of images from various input media or sources to form a single image and to then produce an appropriate rendition of the combined image using any of the various output and display means. For instance, one might wish to merge a portion of an image captured on one medium, such as a positive transparency film, with a portion of an image captured on another medium, such as a color negative film, and produce a single combined image on another medium, such as a video display, so that the entire combined image has an homogeneous and appropriate appearance.
Those skilled in the art will recognize the difficulty of transforming input images to a compatible digital intermediary, as required to achieve the aforementioned color-imaging system capabilities, when disparate sources of input images are to be included as potential inputs to the color-imaging system.
Consider, for example, the problems associated with a color-imaging system which uses highly disparate sources of input images, such as color negative and positive color transparency films. Digitized data derived from these two types of input films would be different in that the densities of negatives increase as a function of increasing exposure, while the densities of positive transparencies decrease as a function of increasing exposure. Furthermore, the contrasts of the two types of films may differ by a factor of three or more, the hues of the imaging dyes may be significantly different, and the colored couplers normally incorporated in negative films produce a minimum density significantly different in both color and level from that of the positive transparency films. Additionally, the inter-layer color-correction characteristics of the negatives are usually significantly different from those of positive transparencies. As a result, without special treatment, digitized data derived from a negative is inappropriate to use with output imaging devices designed to use digitized data from positive transparency. Likewise, without special treatment, digitized data derived from a positive transparency is inappropriate to use with output devices designed to use digitized data from negative films. Moreover, successful exchange, storage, and production of homogeneous-appearing images of merged imaging data is further complicated when other sources of input, such as reflection prints, electronic cameras, etc., are also considered.
Furthermore, in order to optimally display or reproduce color images it is often necessary to correct for variations in overall exposure and color balance due to exposure-control errors of image-capturing devices, variations in the color temperature of taking illuminant, and other factors. These balance adjustments are particularly important for an imaging system which has the previously described capability to merge portions of several images into a composite image. Different balance adjustments for each input image may be necessary in order for the single image to have an homogeneous appearance. A practical color-imaging system should provide a convenient means to apply these balance adjustments. An improved color-imaging system would also provide this capability without requiring references to the input image origins.
Finally, it would be best if the capabilities of the improved color-imaging system are provided in such a way as to preserve the unique advantages of each of the image capturing media. For example, among the advantages of positive color transparency film is its dynamic range, which may exceed a transmittance ratio of 1000 to 1. Among the advantages of color negative film is its extensive exposure latitude.